This is a request for travel support for speakers invited to participate in the Third International Workshop Conference on Human Leucocyte Differentiation Antigens to be held in Oxford, England, September 21-25, 1986. The first meeting of this workshop was convened in Paris in November 1982 and the second in Boston in September 1984. They have been previously supported by the NIH, IUIS, WHO, and INSERM. The Workshop serves three purposes. First, it encourages free worldwide exchange of monoclonal antibodies to human leucocyte differentiation antigens resulting in the orderly characterization of their reactivities and of the antigen they identify. Second, the Workshop encourages in-depth analysis of T lymphocytes, B lymphocytes, stem cells, myelomacrophages and leukaemias using the exchanged reagents. Third, the Workshop establishes a common nomenclature based on the findings of the contributors; representatives of the participants report to a WHO nomenclature committee. The Third Workshop will follow the structure of the previous two. As before, new requests that identify T,B and myeloid antigens will be exchanged and characterized according to centrally-designed protocols. A fourth section will study antibodies to antigens that do not easily fall into the above three categories. In addition to these groups of antibodies will be reagents that have been clustered by the two previous workshops; these will be offered as discrete clusters for detailed analyses of epitopes of the antigens concerned. Studies to be performed on all antibodies include: binding analysis on leucocytes, cell lines and leukaemias; immunohistological studies of lymphoid tissues, lymphomas and other organs; molecular analysis of the antigens; and studies of their function. Given the central role of leucocyte cell surface in cell biology and clinical medicine, the Workshop and Conference will provide a forum for interaction between immunologists, cell biologists, molecular biologists, biochemists, rheumatologists, endocrinologists, oncologists, haematologists, neurologists, allergists, transplantation biologists, and others. It is hoped that new insights into existing materials will be generated, fruitful collaboration developed, and reduplication of research efforts prevented. All of these have been achieved by the previous workshops and interest has already been expressed by more than a hundred laboratories in the Third Workshop.